The present invention pertains generally to the field of thermal insulation material, and more particularly to the field of thermal insulation having a cellulosic component.
The use of cellulosic particulates as thermally insulating material in contemporary construction is well-known. Such insulation takes the form of a free-flowing mixture of small cellulosic particles (about 1-10 mm in diameter) and short cellulosic fibers (about 0.5-3 mm in length), such as that shown in U.S. Pat. No. 4,579,592, wherein the particulates take the form of a low-density collection of cellulosic fibers and cellulosic particles (small chips or splinters). The insulation value arises from cells of trapped air interspersed between the cellulosic particulates; such cells are poor conductors of heat, and are of such a size that convective heat transfer is minimal. The cellulosic insulation is applied either wet or dry to the surface or cavity to be insulated. Smaller areas, such as residential attics, may be insulated by simply pouring the insulation onto the surface to be insulated. Larger areas are often insulated by using special equipment which blows the insulation onto a surface or into a cavity. The mixture may be wettened with an adhesive, allowing the mixture to stick to walls, ceilings, and other such surfaces where the dry mixture alone would not remain on the surface after application.
Cellulosic thermal insulation has several advantages over synthetic insulation materials. It may be made by processing cellulosic materials of either virgin or waste origin by shredding, hammer-milling, or otherwise processing them into a fibrous form. It is biodegradable and its manufacture does not involve the emission of environmentally harmful materials, as the manufacture of synthetic insulation materials often does; the manufacture of fiberglass insulation, for example, generally has the side effect of emitting formaldehyde into the environment. The cellulosic insulation may be rendered flame and/or vermin resistant by treatment with boric acid, mono- and diammonium phosphate, ammonium sulfate, zinc chloride, sodium tetraborate, or other appropriate substances.
However, free-flowing cellulosic insulation has several disadvantages. First, the most common method of application, blowing, requires special equipment. Second, when used in conjunction with adhesives for application to non-horizontal surfaces, application can be messy, time-consuming, and difficult. Third, removal of the mixture is difficult because of the granular (or, if used with an adhesive, foamlike) form of the fibrous mixture, requiring raking, vacuuming, or scraping for removal. All of these disadvantages can be avoided by use of a batt-style thermal insulator, one which may be affixed to the surfaces to be insulated by stapling, nailing, or otherwise attaching it to the surface. Such an insulator may be quickly applied without the use of any special equipment, and it may be quickly peeled away for easy removal or replacement. A batt-style cellulosic insulator would therefore hold several advantages over free-flowing cellulosic insulation that would make the use of cellulosic insulation more attractive when compared to synthetic materials.
As used in the specifications and claims, "batt-style," "batt," or "batting" refers to a blanket-like product composed of loosely layered, non-woven material, as exemplified by fiberglass batt insulation.
Unfortunately, since the individual particulates of cellulosic insulation do not adhere to each other well, a method of forming them into an effective and sturdy batt has heretofore been unknown.
Cotton batts heretofore have been used as sound insulation ("cotton shoddy") underneath carpeting in automobiles and as pipe insulation, but such batts are not effective or sturdy enough for heat insulation in contemporary construction. These batts may have densities of about 200 kg/cubic meter which is too dense to provide effective heat insulation or adequate physical flexibility for contemporary construction.
The difficulty lies in finding a way to make the cellulosic particulates bind in such a way that the resulting batt is durable, but yet has the flexibility necessary for it to be folded or rolled for easy packaging and transportation. Further, the particulates must bind in such a way that the air cells interspersed between the fibers are preserved, if the insulation value of the cellulosic particulates is to be maintained. If the insulation cannot return to its low-density "fluffy" form, with cells of air interspersed between the insulation particulates, the insulating properties are largely lost.
One method of binding cellulosic particulates that is disclosed in the prior art is to mix the cellulosic particulates with thermoplastic particles and apply heat. The thermoplastic component then melts and encapsulates the cellulosic component, whose individual particulates then adhere to each other. Examples of such methods are disclosed in U.S. Pat. Nos. 5,082,605, 5,088,910 and 5,096,046. However, this method produces a product too rigid for easy packaging and transportation, and further does not preserve the insulative value of the cellulosic fibers due to the resulting high density of the product. Similar drawbacks arise from the use of an adhesive to bind the cellulosic fibers.
While the prior art reveals methods of binding cellulosic particulates to a flexible substrate material by the use of an adhesive, e.g. U.S. Pat. No. 4,634,621, such a method is not well-suited for the form of cellulosic particulates used for insulation; such particulates tend to become rigid and inflexible when an adhesive is applied.
Fiber reinforced composites have been manufactured utilizing either a single fiber type or a mixture of fibers to form a nonwoven air-laid batt which either includes thermoplastic fibers or is resinated with a thermoplastic material. This batt is then molded into a preform and maybe injected with resin (e.g. U.S. Pat. Nos. 4,663,225 and 4,812,283).